I was under the impression that we used equal levels for everyone regardless of when they joined and what their level was.
PS4 stat topic says: Rika Level 47, Rune Level 39
Hmm. Well obviously they aren't equal level. What gives? A few other games do similar things. Determining DL level has always been a game-by-game thing. In this case, what you're proposing would reflect FF3 clearly less well than Meeple's method. Generally we go with the best reflection possible.
(Tangent: Generally I think FE is done very poorly in the DL for level, especially in FE10, but accept it as a convenience and due to the sheer difficulty of determining what everyone's level "should" be.)
Besides, you don't use the early classes for the whole game anyways.
You don't? <_< Well, certainly, you don't have to. But you don't have to stick to a late class for every battle after you get it, either. The proportion should be preserved, even if you want to argue some job changing (and uh, we don't usually assume job changing in the DL, see DL Knight being entirely Knight for growth).
(EDIT, elaborating on this for non-FF3 players: order of getting crystals is Wind, Fire, Water, Earth. Crystal of job listed in parentheses)
*checks his first file, grabs his most-used jobs*
Thief (Wi): Level 74
Warrior (Wi): Level 41
Red Mage (Wi): Level 33
Geomancer (F): Level 27
Black Mage (Wi): Level 25
White Mage (Wi): Level 20
Knight (F): Level 19
Devout (E): Level 14
Summoner (E): Level 14
Hmm... a pattern emerges! (Also apparently I hated water crystal jobs.) Let's try my second file. Generally I experimented a bit less with this one, and used classes I didn't use extensively first playthrough, so no Wind jobs.:
Ranger (F): Level 52
Bard (Wa): Level 44
Viking (Wa): Level 39
Monk (Wi): Level 37 *never used this after getting the Water crystal*
Dark Knight (Wa): Level 35
Ninja (E): Level 29
Black Belt (E): Level 26
Magus (E): Level 22
Sage (E): Level 18
Oh gee look what four classes are at the bottom. Note also that I NEVER USED ANYTHING EXCEPT THESE once I got them, so everything above them is actually underrated.